Methyl acetate is used industrially in petrochemical processes, particularly as a feed for the production of acetic acid and/or acetic anhydride.
The commercial production of acetic acid is operated as a homogeneous liquid-phase process in which the carbonylation reaction is catalysed by a Group VIII noble metal such as rhodium or iridium and an alkyl iodide such as methyl iodide. The main drawbacks of this process are the use of iodide which can lead to corrosion problems and the difficulties associated with separation of the products and catalyst components from a single phase. Both of these drawbacks could be overcome if a heterogeneous gas phase process using an iodide free solid catalyst could be developed.
EP-A-0 596 632 describes a vapour phase process for the carbonylation of methanol to produce acetic acid in the presence of a modified mordenite catalyst at high temperatures and pressures.
WO 01/07393 describes a process for the catalytic conversion of a feedstock comprising carbon monoxide and hydrogen to produce at least one of an alcohol, ether and mixtures thereof and reacting carbon monoxide with the at least one of an alcohol, ether and mixtures thereof in the presence of a catalyst selected from solid super acids, heteropolyacids, clays, zeolites and molecular sieves, in the absence of a halide promoter, under conditions of temperature and pressure sufficient to produce at least one of an ester, acid, acid anhydride and mixtures thereof. However, the use of zeolites to catalyse the carbonylation reaction is not exemplified.
WO 2005/105720 describes a process for production of a carboxylic acid and/or an ester or anhydride thereof by carbonylating an aliphatic alcohol or reactive derivative thereof with carbon monoxide in the substantial absence of halogens in the presence of a modified mordenite catalyst at a temperature in the range 250-600° C. and a pressure in the range 10 to 200 bar. The use of dimethyl ether as a feedstock is not exemplified.
WO 2006/121778 describes a process for the production of a lower alkyl ester of a lower aliphatic carboxylic acid by carbonylating under substantially anhydrous conditions a lower alkyl ether with carbon monoxide in the presence of a mordenite or ferrierite catalyst. According to this patent application, the carbonylation process is run at temperatures at or below 250° C., and preferably from about 150 to about 180° C. to minimise by-product formation.
In Angewandte Chemie, Int. Ed. (2006), 45(10), 1617-1620, which describes the zeolite-catalysed carbonylation of dimethyl ether, it is demonstrated that at 165° C., increasing the concentration of dimethyl ether has no effect on the space time yield to methyl acetate product.
In view of the above-mentioned prior art, there remains the need for a heterogeneous gas phase process for the production of methyl acetate from dimethyl ether under substantially anhydrous conditions using a zeolite catalyst which is superior to the other processes using a carbonylatable reactant as a feed.